Anomalies in Cosmic Ray Composition: Explanation Based on Mass to Charge Ratio

TL;DR

This paper investigates cosmic ray composition anomalies by analyzing how the mass-to-charge ratio influences particle injection in shock acceleration, supported by hybrid simulations that align with observational data.

Contribution

It introduces a simulation-based explanation for elemental anomalies in cosmic rays, emphasizing the role of mass-to-charge ratio in particle injection processes.

Findings

Simulation results match AMS-02 and Pamela data.

Injection rates depend on mass-to-charge ratio.

Intrinsic shock mechanisms explain elemental anomalies.

Abstract

High precision spectrometry of galactic cosmic rays (CR) has revealed the lack of our understanding of how different CR elements are extracted from the supernova environments to be further accelerated in their shocks. Comparing the spectra of accelerated particles with different mass to charge ratios is a powerful tool for studying the physics of particle injection into the diffusive shock acceleration (DSA). Recent AMS-02 demonstration of the similarity of He/$p$, C/$p$, and O/$p$ rigidity spectra has provided new evidence that injection is a mass-to-charge dependent process. We performed hybrid simulations of collisionless shocks and analyzed a joint injection of $p$ and He$^{2+}$ in conjunction with upstream waves they generate. By implication, our results equally apply to C and O fully ionized ions, since they have similar mass to charge ratios. By convolving the time-dependent injection rates of $p$ and He, obtained from the simulations, with a decreasing shock strength over the active life of SNRs, we generate the integrated SNR spectra for $p$ and He. These spectra are consistent with the AMS-02 and Pamela data and earlier theoretical predictions. Our interpretation of the elemental anomaly is therefore intrinsic to collisionless shock mechanisms and does not require additional assumptions, such as the contributions from several different SNRs, their inhomogeneous environments or acceleration from grains.